If you are looking at consultants...

Remember, one of the most important concepts in strategy is focus.
Any strategic planning consultant who says "I do strategic planning and..." is not focused. They are just fooling around when it comes to strategic planning.
You wouldn't go to a brain surgeon who says "I do brain surgery and plastic surgery." So why work with someone who does something else, like marketing, operations or teambuilding consulting? Your company deserves the best, not an amateur.
Here are some useful questions for when you are choosing a consultant:

1. How many strategic plans did you work on last year? In the past 10 years?
2. What results do your clients get? Can I talk to them?
3. What else do you do besides strategic planning? Will you try to sell that to me?
4. How are you different from other people who do strategic planning?
5. Why do you think there is a fit between you and my company?
6. Do you work with my competitors? How do I know you won't share my data with them?

On that last question - you want to avoid consultants who work with your competitors. The worst strategy is the one that looks just like your competitors - and using the same consultant is a sure-fire way to get that.